Google Docs Tab iFrame

I have created a few iFrame tabs that are working well to open things like our help desk login ect. I am having an issue though creating one to open our google docs page. The tab appears but the page never loads. In fact it refuses to load any google pages. I know the code is right because if I change the url to say cnn.com it works just fine. Any Ideas why it will not load any page from google?